1. Field of the Invention
The invention relates to auxiliary power units (APUs), starters, generators, motors, and cooling systems for aircraft and, more particularly, to an integrated auxiliary power unit (APU), starter-generator-motor (SGM), and vapor cycle cooling system (VCCS) for an aircraft.
2. Discussion of the Related Art
Some conventional business and commercial aircraft are equipped with auxiliary power units (APUs). A conventional aircraft APU is based on a turbine engine and provides pneumatic power and mechanical shaft power output. The mechanical shaft can be used to drive accessories such as mechanically-driven pneumatic compressors, refrigerant compressors, hydraulic pumps, fuel pumps, electrical generators, and/or electrical starter-generators, or can be driven by accessories such as a starter or electrical starter-generator. When the mechanical shaft power drives a generator, it provides electrical power to the aircraft electrical systems for such tasks as environmental control, lighting, powering of electronics, main engine starting, etc. Pneumatic power can be provided from the internal compressor inside the APU's turbine engine or a mechanically-driven pneumatic compressor. Pneumatic power is typically used with an air cycle cooling system (ACCS).
Instead of an air cycle cooling system, some aircraft include a vapor cycle cooling system (VCCS) to air condition the aircraft cabin. The VCCS includes a refrigerant compressor, a condenser, a condenser fan, and evaporator fans. The VCCS compressor is typically mechanically-driven and the condenser fan and evaporator fans are typically electrically-powered for the VCCS to provide aircraft cabin cooling. To that end, when the APU is operating, the APU can provide the capability to mechanically-drive the VCCS compressor. When the APU is not operating and the SGM is in motor mode, the SGM can receive external electrical power to mechanically drive the VCCS compressor. Electrical power to operate the VCCS condenser fan and VCCS evaporator fans can be provided by the SGM when it is in generator mode or by an external electrical power source when the SGM is in motor mode.
The APU and VCCS compressor would be attached to a starter-generator-motor apparatus (SGM). The SGM is operable in any of a starter mode, a generator mode, or a motor mode. In the starter mode, the SGM can mechanically drive and start the APU; in generator mode, the SGM is driven by the APU and produces electrical power that can be delivered to the aircraft electrical system (including to power the VCCS condenser fan and VCCS evaporator fans); in the motor mode, the SGM can receive electrical power from an external electrical power source and be electrically-driven to mechanically drive the VCCS compressor. SGMs are known in the art, and are described in U.S. Pat. Nos. 4,803,376 and 6,002,219.